1,720,957 research outputs found
Chordal Based Error Function for 3D Pose-Graph Optimization
No full textPose-Graph Optimization (PGO) is a well-known problem in the Robotics community. Optimizing a graph means finding the configuration of the nodes that best satisfies the edges. This is generally achieved using iterative approaches that refine a current solution until convergence. Nowadays, Iterative Least-Squares (ILS) algorithms such as Gauss-Newton (GN) or Levenberg-Marquardt (LM) are dominant. Common to all these implementations is the influence of the error function used to measure the difference between prediction and observation. The smoother the error function is, the better the convergence properties of the system become, resulting in an increased convergence basin and more stable behavior. In this work, we propose an alternative error function based on a variant of the Frobenious norm between transformation matrices. The proposed approach leads to a larger convergence basin and to numerical properties in the Jacobian computation that can potentially speed-up the system. In contrast with some existing approximations, our formulation allows to model isotropic and anistropic noise covariances. To validate our conjectures, we present an extensive comparative analysis between our approach and one of the most used error function that computes the distance in the unit-quaternion space
Exploiting Non-Minimal Parametrizations in Graph-Based SLAM
No full textTo date, technology is in constant development, and researchers all over the world are pushing its boundaries every day further. In particular, Robotics is one of the fields that is currently in great expansion, entering into our daily lives in many ways - e.g. autonomous driving cars, service robots, video-games.
Intelligent systems have several basic requirements to safely accomplish tasks in the real world. Among them we include i) having a digital map of the environment in which these agents are placed and ii) the ability to localize themselves in such a map. The problem of building a map while estimating the agent’s pose is known in Robotic research as Simultaneous Localization and Mapping (SLAM). As an example, an autonomous car that is asked to reach a location and, thus, has to traverse the city, needs to know the configuration of its surroundings in real-time, including the position of pedestrians, cars, bikes, and every other dynamic (or static) obstacle. Global positioning infrastructures - e.g. GPS - do not provide information on the surroundings and their signal is not always available. For this reason, other sensing modalities are generally used to accomplish such tasks efficiently.
This thesis focuses on SLAM, investigating ways to increase the robustness and scalability of the solutions to this problem. More in detail, we will aim the attention to graph- based SLAM systems, which represent the most common choice in state-of-the-art pipelines. In such formalization, Least-Squares optimization represents the foundation of the entire estimation process, allowing it to achieve good accuracy without violating the real-time constraint of Robotic applications.
In particular, we will investigate how non-minimal over-parametrizations of the optimization entities contribute to the accuracy, robustness, and scalability of the system. Traditionally, minimal parametrizations are used in the Least-Squares estimation process at different levels: i) to apply small increments to state variables, ii) to represent measurements, and iii) to express local distances between prediction and measurement. Still, such minimal parametrizations might be hard to compute, leading to complex mathematical derivations in the minimization algorithm. Conversely, extended parametrizations introduce additional parameters in the estimation process, possibly leading to a relaxed version of the original problem which can be solved more easily.
Leveraging on this concept, we introduced a non-minimal error function in the context of global optimization, aiming to enlarge the converge basin and the overall robustness to noise. Then, we addressed how the map is represented, exploiting a novel extended landmark formalization that allows representing multiple geometric primitives as a unique object. Finally, we present a novel Least-Square optimization framework, which is specifically designed for SLAM pipelines and that can be easily extended to accommodate new solutions - such as the ones previously proposed.
All of our contributions are open-source and publicly available to the research community.
We believe that this is an important aspect of research, allowing to easily reproduce the results obtained in the proposed experiments while fostering the collaboration with other members of the community
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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